In integrated circuit fabrication, dopants are frequently introduced into semiconductor substrates to provide the semiconductor substrate with certain electrical characteristics. High-energy implants (e.g., implants using an implant energy in excess of about 150 keV) are an increasingly important method for introducing dopants into semiconductor substrates. At these high energies, the dopant profile is tailored to provide the desired concentration of dopant within the desired distance from the surface of the semiconductor substrate.
It is well recognized, however, that such high-energy implants, particularly when used in combination with high dopant doses, may lead to certain long-term undesirable defects. For instance, it is well recognized that high-energy implants tend to form long dislocation dipoles (also referred to as threading dislocations) after a furnace anneal of the implanted substrates. These dislocations are typically generated in the substrate at the approximate depth of the mean projected range of the implanted ions. Moreover, the dislocations tend to migrate to the substrate surface and have been found to cause high junction leakage currents, Gate Oxide Integrity issues and other electrical problems.
It has been observed that the threading dislocation density caused by high energy Boron implants is much greater than other implant species and that the threading dislocations are generated under a variety of different anneal conditions (e.g., a post implant anneal conducted at 900° C. for about 30 minutes). It has been observed that the threading dislocation density has strong dose dependence, with a maximum defect density observed at Boron doses ranging from about 5E13 atoms/cm2 to about 2E14 atoms/cm2, with a peak defect density at a Boron dose of about 1E14 atoms/cm2.
The industry has attempted to address these threading dislocations in a number of different ways. First, the industry attempted reducing or increasing the Boron implant dose to a value outside of the range that brings about the aforementioned maximum defect density. This method poses several difficulties or barriers to include requiring devices or components to operate within a different doping profile (e.g. dopant well) than intended or designed; this is especially true to High Voltage devices and components where the well doping sets breakdown characteristics for the component. Second, the industry proposed a two-step anneal wherein the substrate is first annealed at a lower temperature for a longer time period and then annealed at the typical temperature. The two-step anneal reduced the density of threading dislocations in Boron-implanted substrates, however, the 20 or so hour anneal is simply too long to be practical in commercial processes for semiconductor processing.
Consequently, processes that reduce the threading dislocations caused by high-energy implants and that are compatible with commercial processes for device fabrication are sought.